1. Field of the Invention
The present invention relates to an abnormality detection apparatus of a work holder that grips a flat work in a punch press machine or a shearing machine or the like.
2. Background Art
On a sheet metal processing machine such as a punch press or the like, the edge of work loaded on a table is gripped by a work holder and processing is carried out by positioning the process position of the gripped work in the process part of the machine by moving the work holder along X and Y axes.
In this way, the process position of the work is delivered to the process part by movement of the work in the X and Y axes but for a number of reasons, the work may separate from the work holder. If this occurs, exact processing can not be carried out on the work and the work itself may fly off the table thus representing a danger to the operator. Likewise the problem of machine durability may arise with damage to other parts of the machine.
Conventionally, mechanisms preventing separation of the work had been devised but in the following cases, the possibility of work separation remained:
1) When large scale work (heavy work) is moved at high speed, the inertia of the work increases and the gripping force of the work holder is unable to counteract the work inertia. PA1 2) Whenever the punch tool catches in the work while processing and the work holder is moved in that state. PA1 3) In particular, in the processing of thin work, whenever the connector part (called the microjoint) that connects the product work formed from the punch process and the material work catches on the ball member of the table or another part and the work holder is moved in that state.